Sleep apnea is a potentially life-threatening breathing disorder characterized by brief interruptions of breathing during sleep. There are two types of sleep apnea: central and obstructive. Central sleep apnea, which is less common, occurs when the brain fails to send the appropriate signals to the breathing muscles to initiate respirations. Obstructive sleep apnea occurs when air cannot flow into or out of the person's nose or mouth although efforts to breathe continue. In a given night, the number of involuntary breathing pauses or “apneic events” may be as high as 20 to 60 or more per hour. Sleep apnea can also be characterized by choking sensations. The frequent interruptions of deep, restorative sleep often leads to excessive daytime sleepiness and may be associated with an early morning headache. Early recognition and treatment of sleep apnea is important because it may be associated with irregular heartbeat, high blood pressure, heart attack, and stroke.
Various forms of positive airway pressure during sleep can be an effective form of therapy for the apnea sufferer. Ventilation can be applied in the form of continuous positive airway pressure (CPAP), in which positive pressure is maintained in the airway throughout the respiratory cycle; bi-level positive airway pressure system, in which positive pressure is maintained during inspiration but reduced during expiration; and intermittent (non-continuous) positive pressure (IPPB), in which pressure is applied when an episode of apnea is sensed. In such procedures, a patient wears a mask over the nose during sleep, and pressure from an air blower forces air through the nasal passages. Typically, such masks receive a gas supply line that delivers gas into a chamber formed by wall of the mask and the patient's face. The walls are usually semi-rigid and have a face-contacting portion include an aperture that is aligned with the patient's nostrils. The face-contacting portion can include a soft, resilient elastomeric material that can conform to various facial contours. The mask is normally secured to the patient's head by straps. The straps are adjusted to pull the mask against the face with sufficient force to achieve a gas tight seal between the mask and the patient's face but not so tight as to be uncomfortable. Gas is thus delivered to the mask and into the patient's nasal passages.
Problems often arise with masks of the above configuration. For example, the face-contacting portion may apply excessive pressure to the wearer's face resulting in discomfort and possibly skin irritation. This can occur because the face-contacting portion has to distort beyond its normal range of elasticity to conform to certain facial contours, which requires the application of excessive forces. In some cases these excessive pressures and forces may cause the face to distort to conform to the face-contacting portion, which can increase wearer discomfort, resulting in facial soreness and ulceration.